S Number (wool) - Metric Yarn Count

Metric Yarn Count

The worsted count was only a rough measurement and has been replaced by more exact methods such as the metric yarn count. However for fine wool, the memory of the older system survives in the S numbers which have a very rough correspondence to worsted count. In other words, fiber that yielded about 80 worsted hanks is roughly comparable to fiber designated as 80s using the S numbers. The critical difference is that while the worsted number was an indirect measure (and a rough one at that) of yarn thickness, the S number is a direct (and precise) measurement of the thickness of the fiber. The S number of fiber, and hence of yarn, fabric, or garments made of that fiber, is determined using the international standard promulgated by the International Wool Textile Organisation (IWTO).